The replication of DNA occurs within the nucleus of eukaryotic cells (cells that contain a nucleus and organelles).
DNA begins when the enzyme called helicase begins to unzip the two strands that create the double helix. Single-stranded binding proteins (SSBs) then stabilize the unzipped strands. Nucleotide base pairs are matching along the open strands. The leading strand is synthesized in the 5' --> 3' direction continuously using the enzyme DNA polymerase. The lagging strand is created in fragments (called Okazaki fragments) in the opposite direction. The Okazaki fragments are initiated using primase that begins a short RNA primer. The RNA primers are then enlongated using DNA polymerase. The small fragments grow into one another and are linked via the enzyme called ligase. Growth of each strand continues until the DNA fully unzips and two double helices result from the one original DNA molecule.